1. Field of the Invention
The invention relates to a joint for duplex pipes where an outer pipe, an inner pipe provided inside of the outer pipe, and ribs for connecting both pipes are integrally formed as one body through an extruding process or drawing process, and relates to a method of brazing the joint to a duplex pipe. Further, the invention relates to an air-conditioning apparatus for a vehicle, which suppresses transmission of vibration from an engine and compressor to an evaporator, and reduces noise in the passenger's room.
2. Description of the Related Art
As is well known, a duplex pipe is provided with an outer pipe for passing a first fluid and an inner pipe provided inside of the outer pipe for passing a second fluid. Being classified by manufacturing methods, there are two types of duplex pipes.
One type of the duplex pipe is such duplex pipes where an outer pipe and an inner pipe are produced separately and independently, and the inner pipe is inserted into the outer pipe, and the outer pipe is subjected to a drawing process so that projections projecting on the inner wall of the outer pipe are pressed to the outer wall of the inner pipe.
The other type is such a duplex pipe where the outer pipe, the inner pipe and the ribs connecting both are integrally formed by the extruding process or drawing process. Recently, from the viewpoint of lowering the prime cost of production, the duplex pipes of the latter type of connecting the outer pipe and the inner pipe via the ribs have been frequently practiced.
The Japanese Patent No. 2595578 describes a joint for a pipe system having a duplex structure of an outer-side hose and an inner-side hose made of rubber.
However, the joint structure described in the above publication can be applied to a case where the outer pipe and the inner pipe are separately composed, but cannot be applied to the duplex pipes in which the outer pipe, the inner pipe and the ribs are integrally formed.
The duplex pipes and the joint for the duplex pipes may be utilized in a cooling cycle for an air conditioning apparatus.
In the cooling cycle for the air-conditioning apparatus for the vehicle, as shown in FIG. 26, a gas coolant heated to a high temperature and pressurized to a high pressure by the compressor 1101 flows to the condenser 1102, and becomes a high pressure liquid coolant or gas-liquid mixture coolant after exchanging heat with the atmosphere. This high pressure coolant becomes a low temperature and low pressure liquid coolant or low gas-liquid mixture coolant through adiabatic expansion by the expansion valve 1106 after separation into a gas and liquid in the liquid tank 1103. This low pressure coolant flows to the evaporator 1104 installed in the passenger's room, and cools the air in the compartment by exchanging heat with the air, and returns to the compressor 1101 as a low pressure gas coolant.
In such a cooling cycle, the compressor 1101 and the condenser 1102 are connected by the high pressure coolant pipe 1105a, the condenser 1102 and the liquid tank 1103 are connected by the high pressure coolant pipe 1105b, the liquid tank 1103 and the evaporator 1104 are connected by the high pressure coolant pipe 1105c, and the evaporator 1104 and the compressor 1101 are connected by the low pressure coolant pipe 1110. Additionally, at the connecting portions of the pipe for coolant 1105a through 1105c, and 1110, pipe joints are used, as a result, in the whole of the cooling cycle, and in total eight pipe joints 1121 through 1128 are installed. In the Figure, the numerals 1131 and 1132 show the pipe for absorbing vibration.
Incidentally, the driving force of the engine is transmitted to the compressor 1101 through a belt which is not shown, and the vibration of the engine travels to the compressor 1101. Further, the compressor 1101 generates a pulsating sound when taking in, compressing and discharging the coolant.
Therefore, the vibration and pulsation of the engine and compressor 1101 gives more vibration to the low pressure coolant pipe 1110 provided to connect the compressor 1101 and the evaporator 1104, and further this travels to the evaporator 1104 through this coolant pipe 1110 and makes a vibration thereon, as a result, which possibly causes noise in the passenger's room.
Since there are a total of eight pipe joints installed at the connecting portions of coolant pipe 1105a through 1105c, and 1110 in the whole of cooling cycle as explained above, there are many pipe joints which possibly causes leakage of the coolant, and causes a problem that many man-hours are required to perform leakage inspection after installing the pipe.
Further, as explained above, the high pressure liquid coolant or gas-liquid mixture coolant is supplied from the condenser 1102 to the expansion valve 1106, in order to stabilize the supply of the liquid coolant to this expansion valve 1106 and to enhance the cooling capacity, it is preferable to use a sub-cooling process in which providing proper over-cooling at around the outlet of the condenser 1102 brings sufficient liquid coolant. To adopt this method, the condenser 1102 inevitably becomes large in scale.
Further, the low pressure gas coolant is supplied from the evaporator 1104 to the compressor 1101, and in order to prevent liquid compression in the compressor 1101 and to enhance the cooling capacity, it is preferable to use a superheating method in which providing proper overheating at around the outlet of the evaporator 1104 brings sufficient gas coolant. To adopt this method, the evaporator 1104 inevitably becomes large in scale, at the same time, and the performance is degraded by worsening dividing flow.
Further, space is required to ensure that two kinds of pipe, high pressure coolant pipe 1105a through 1105c and low pressure coolant pipe 1110, are separately installed, however, there is a requirement that a narrow engine compartment be used effectively if possible.